Binder composition for non-aqueous secondary battery electrode, slurry composition for non-aqueous secondary battery electrode, electrode for non-aqueous secondary battery, and non-aqueous secondary battery

ABSTRACT

A binder composition for a non-aqueous secondary battery electrode contains water and a polymer that includes an aromatic vinyl monomer unit, a conjugated diene monomer unit, and a hydrophilic monomer unit. The polymer has a median diameter of not less than 50 nm and not more than 800 nm, and the proportional content of the hydrophilic monomer unit in the polymer is not less than 4.0 mass % and not more than 20 mass %. Moreover, the polymer has a loss tangent tan δ of not less than 0.001 and less than 0.40 and a loss modulus G″ of 1,600 kPa or less.

TECHNICAL FIELD

The present disclosure relates to a binder composition for a non-aqueoussecondary battery electrode, a slurry composition for a non-aqueoussecondary battery electrode, an electrode for a non-aqueous secondarybattery, and a non-aqueous secondary battery.

BACKGROUND

Non-aqueous secondary batteries (hereinafter, also referred to simply as“secondary batteries”) such as lithium ion secondary batteries havecharacteristics such as compact size, light weight, high energy density,and the ability to be repeatedly charged and discharged, and are used ina wide variety of applications. Consequently, in recent years, studieshave been made to improve battery members such as electrodes for thepurpose of achieving even higher non-aqueous secondary batteryperformance.

An electrode used in a secondary battery such as a lithium ion secondarybattery normally includes a current collector and an electrode mixedmaterial layer (positive electrode mixed material layer or negativeelectrode mixed material layer) formed on the current collector. Thiselectrode mixed material layer is formed by, for example, applying aslurry composition containing an electrode active material, abinder-containing binder composition, and so forth onto the currentcollector, and then drying the applied slurry composition.

In order to further improve the performance of secondary batteries,attempts have been made in recent years to improve binder compositionsused in electrode mixed material layer formation. As one specificexample, Patent Literature (PTL) 1 proposes an aqueous bindercomposition for a battery electrode containing a copolymer latex, afeature of which is that with regards to dynamic viscoelasticity of afilm, the copolymer latex has a curve on which, when the maximum peaktemperature of a loss coefficient tan δ is taken to be Tp (° C.), Tp ispresent within a range of −20° C. to 60° C., tan δ (Tp) thereof ispresent within a range of 4.0×10⁻¹ to 1.0×10⁰, and a temperature rangein which tan δ is 60% or more of tan δ (Tp) is 35° C. or more. Thecopolymer contained in this binder composition is obtained throughemulsion polymerization of a monomer composition containing 12 mass % to50 mass % of an aliphatic conjugated diene monomer, 1.0 mass % to 10mass % of a carboxylic acid alkyl ester monomer, 0.1 mass % to 10 mass %of an ethylenically unsaturated carboxylic acid monomer, and 30 mass %to 86.9 mass % of monomers that are copolymerizable with these monomers.This binder composition has high binding capacity even when used in awide range of environment temperatures and can preserve electrodestructure during charging and discharging.

CITATION LIST Patent Literature

PTL 1: JP2017-126456A

SUMMARY Technical Problem

From a viewpoint of increasing secondary battery producibility, it isnecessary for a binder composition to have a polymer uniformly dispersedtherein even after stationary storage for a certain period afterproduction. Moreover, in an electrode formed using a binder composition,it is necessary for a mixed material layer and a current collector thatare constituents of the electrode to be bound with high binding strengtheven at high temperature in a production process of a secondary battery.In other words, it is necessary for a binder composition to enableformation of an electrode that displays high peel strength even uponexposure to high temperature. Furthermore, it is preferable that asecondary battery including an electrode formed using a bindercomposition has low internal resistance.

However, it has not been possible to simultaneously achieve uniformityof a polymer in a binder composition after stationary storage(hereinafter, also referred to as “stationary stability”), increasedpeel strength of an electrode after exposure to high temperature, andreduced internal resistance of an obtained secondary battery tosufficiently high levels with the conventional binder described above.

Accordingly, one object of the present disclosure is to provide a bindercomposition for a non-aqueous secondary battery electrode that hasexcellent stationary stability and can form an electrode havingexcellent peel strength after exposure to high temperature and anon-aqueous secondary battery having low internal resistance.

Another object of the present disclosure is to provide a slurrycomposition for a non-aqueous secondary battery electrode that can forman electrode having excellent peel strength after exposure to hightemperature and a non-aqueous secondary battery having low internalresistance.

Yet another object of the present disclosure is to provide an electrodefor a non-aqueous secondary battery that has excellent peel strengthafter exposure to high temperature and can form a secondary batteryhaving low internal resistance and also to provide a non-aqueoussecondary battery that has low internal resistance.

Solution to Problem

The inventors conducted diligent investigation with the aim of solvingthe problems set forth above. The inventors discovered that when abinder composition contains a polymer that satisfies a specific chemicalcomposition and median diameter and that has a loss tangent tan δ andloss modulus G″ within specific ranges as measured by a specific method,this binder composition has excellent stationary stability and can beused to obtain an electrode having excellent peel strength afterexposure to high temperature and a secondary battery having low internalresistance. In this manner, the inventors completed the presentdisclosure.

Specifically, the present disclosure aims to advantageously solve theproblems set forth above, and a presently disclosed binder compositionfor a non-aqueous secondary battery electrode comprises: a polymerincluding an aromatic vinyl monomer unit, a conjugated diene monomerunit, and a hydrophilic monomer unit; and water, wherein the polymer hasa median diameter of not less than 50 nm and not more than 800 nm,proportional content of the hydrophilic monomer unit in the polymer isnot less than 4.0 mass % and not more than 20 mass %, and the polymerhas a loss tangent tan δ of not less than 0.001 and less than 0.40 and aloss modulus G″ of 1,600 kPa or less. The binder composition containinga polymer that satisfies a specific chemical composition and mediandiameter and that has a loss tangent tan δ and loss modulus G″ withinspecific ranges as measured by a specific method in this manner hasexcellent stationary stability, and by using this binder composition, itis possible to obtain an electrode having excellent peel strength afterexposure to high temperature and a secondary battery having low internalresistance.

Note that a “monomer unit” of a polymer referred to in the presentdisclosure is a “repeating unit derived from that monomer that isincluded in a polymer obtained using the monomer”.

Also note that the “median diameter” of a polymer can be measured inaccordance with a method described in the EXAMPLES section of thepresent specification.

Moreover, the proportional content of each type of monomer unit in apolymer can be measured by ¹H-NMR.

Furthermore, the “loss tangent tan δ” and “loss modulus G″” of a polymercan be measured in accordance with a method described in the EXAMPLESsection of the present specification.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the conjugated diene monomer unit includedin the polymer is preferably a unit derived from 1,3-butadiene monomer.When the conjugated diene monomer unit included in the polymer is a unitderived from 1,3-butadiene monomer, it is possible to increasepreservation stability of a slurry composition for a non-aqueoussecondary battery electrode that is obtained using the bindercomposition for a non-aqueous secondary battery electrode. Moreover,through a binder composition containing a polymer that includes a unitderived from 1,3-butadiene monomer as a conjugated diene monomer unit,it is possible to form an electrode having even better peel strengthafter exposure to high temperature.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, gel content measured when the polymer isimmersed in tetrahydrofuran is preferably not less than 35 mass % andnot more than 60 mass %. Through the gel content measured when thepolymer is immersed in tetrahydrofuran being not less than 35% and notmore than 60%, it is possible to appropriately control initial viscosityin production of a slurry composition using the binder composition andto further enhance battery characteristics of a secondary battery thatis ultimately obtained.

Note that the “gel content” of a polymer can be measured in accordancewith a method described in the EXAMPLES section of the presentspecification.

In the presently disclosed binder composition for a non-aqueoussecondary battery electrode, the polymer preferably includes an aromaticvinyl block region formed of aromatic vinyl monomer units. Through thebinder composition containing a polymer that includes an aromatic vinylblock region formed of aromatic vinyl monomer units, it is possible toobtain an electrode having even better peel strength after exposure tohigh temperature and a secondary battery having even lower internalresistance by using this binder composition. When a polymer is said to“include a block region formed of monomer units” in the presentspecification, this means that “a section where only such monomer unitsare bonded in a row as repeating units is present in the polymer”.

Moreover, the present disclosure aims to advantageously solve theproblems set forth above, and a presently disclosed slurry compositionfor a non-aqueous secondary battery electrode comprises: an electrodeactive material; and any one of the binder compositions for anon-aqueous secondary battery electrode set forth above. When a slurrycomposition contains the binder composition for a non-aqueous secondarybattery electrode set forth above in this manner, it is possible toimprove peel strength after exposure to high temperature (hereinafter,also referred to as “high-temperature peel strength”) of an electrodeformed using the slurry composition and to reduce internal resistance ofa secondary battery.

Furthermore, the present disclosure aims to advantageously solve theproblems set forth above, and a presently disclosed electrode for anon-aqueous secondary battery comprises an electrode mixed materiallayer formed using the slurry composition for a non-aqueous secondarybattery electrode set forth above. By using the slurry composition for anon-aqueous secondary battery electrode set forth above in this manner,it is possible to obtain an electrode that has excellenthigh-temperature peel strength and can form a secondary battery havinglow internal resistance.

Also, the present disclosure aims to advantageously solve the problemsset forth above, and a presently disclosed non-aqueous secondary batterycomprises a positive electrode, a negative electrode, a separator, andan electrolyte solution, wherein at least one of the positive electrodeand the negative electrode is the electrode for a non-aqueous secondarybattery set forth above. By using the electrode for a non-aqueoussecondary battery set forth above, it is possible to obtain anon-aqueous secondary battery having low internal resistance.

Advantageous Effect

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery electrode that hasexcellent stationary stability and can form an electrode havingexcellent peel strength after exposure to high temperature and anon-aqueous secondary battery having low internal resistance.

Moreover, according to the present disclosure, it is possible to providea slurry composition for a non-aqueous secondary battery electrode thatcan form an electrode having excellent peel strength after exposure tohigh temperature and a non-aqueous secondary battery having low internalresistance.

Furthermore, according to the present disclosure, it is possible toprovide an electrode for a non-aqueous secondary battery that hasexcellent peel strength after exposure to high temperature and can forma secondary battery having low internal resistance and also to provide anon-aqueous secondary battery that has low internal resistance.

DETAILED DESCRIPTION

The following provides a detailed description of embodiments of thepresent disclosure.

The presently disclosed binder composition for a non-aqueous secondarybattery electrode can be used in production of the presently disclosedslurry composition for a non-aqueous secondary battery electrode.Moreover, a slurry composition for a non-aqueous secondary batteryelectrode that is produced using the presently disclosed bindercomposition for a non-aqueous secondary battery electrode can be used inproduction of an electrode of a non-aqueous secondary battery such as alithium ion secondary battery. Furthermore, a feature of the presentlydisclosed non-aqueous secondary battery is that the presently disclosedelectrode for a non-aqueous secondary battery, which is formed using thepresently disclosed slurry composition for a non-aqueous secondarybattery electrode, is used therein.

Note that the presently disclosed binder composition for a non-aqueoussecondary battery electrode, slurry composition for a non-aqueoussecondary battery electrode, and electrode for a non-aqueous secondarybattery are preferably for a negative electrode, and the presentlydisclosed non-aqueous secondary battery is preferably a non-aqueoussecondary battery in which the presently disclosed electrode for anon-aqueous secondary battery is used as a negative electrode.

Binder Composition for Non-Aqueous Secondary Battery Electrode

The presently disclosed binder composition for a non-aqueous secondarybattery electrode contains water and a polymer that includes an aromaticvinyl monomer unit, a conjugated diene monomer unit, and a hydrophilicmonomer unit. Moreover, features of the polymer are that the mediandiameter of the polymer is not less than 50 nm and not more than 800 nmand that the proportional content of hydrophilic monomer units in thepolymer is not less than 4.0 mass % and not more than 20 mass %.Furthermore, features of the polymer are that the polymer has a losstangent tan δ of not less than 0.001 and less than 0.40 and a lossmodulus G″ of 1,600 kPa or less as measured in accordance with a methodsubsequently described in the EXAMPLES section.

As a result of the polymer satisfying a specific chemical compositionand median diameter and having a loss tangent tan δ and loss modulus G″within specific ranges as measured by a specific method, the presentlydisclosed binder composition has excellent stationary stability and canbe used to form an electrode having excellent peel strength afterexposure to high temperature and a secondary battery having low internalresistance.

<Polymer>

The polymer is a component that functions as a binder and that holdscomponents such as an electrode active material in an electrode mixedmaterial layer formed using a slurry composition containing the bindercomposition so as to prevent detachment of these components from theelectrode mixed material layer.

Moreover, the polymer is water-insoluble particles. Note that whenparticles of a polymer are referred to as “water-insoluble” in thepresent disclosure, this means that when 0.5 g of the polymer isdissolved in 100 g of water at a temperature of 25° C., insolublecontent is 90 mass % or more.

<<Median Diameter of Polymer>>

The median diameter of the polymer is required to be not less than 50 nmand not more than 800 nm. Moreover, the median diameter of the polymeris preferably 100 nm or more, and more preferably 200 nm or more, and ispreferably 500 nm or less. When the median diameter of the polymer isnot less than any of the lower limits set forth above, high-temperaturepeel strength of an obtained electrode can be improved, and internalresistance of an obtained secondary battery can be reduced. Moreover,when the median diameter of the polymer is not more than any of theupper limits set forth above, stationary stability of the bindercomposition can be increased.

The median diameter of the polymer can be controlled by alteringconditions in production of the polymer or by performing aclassification step of centrifugal separation, filtration, or the likewith respect to a polymerized product satisfying an arbitrary particlediameter distribution, but is not specifically limited to beingcontrolled in this manner. For example, in a subsequently describedproduction method that includes a step of performing phase-inversionemulsification and graft polymerization with respect to polymerparticles each constituting a core, the median diameter of the polymercan be increased by increasing the concentration of the polymerparticles in phase-inversion emulsification, subjecting polymerparticles having a large molecular weight to phase-inversionemulsification, and so forth.

<<Loss Tangent tan δ of Polymer>>

The loss tangent tan δ of the polymer is required to be not less than0.001 and less than 0.40, and is preferably 0.37 or less. When the losstangent tan δ is within any of the ranges set forth above,high-temperature peel strength can be increased. Note that the losstangent tan δ of the polymer can be adjusted based on the chemicalcomposition of the polymer, production conditions of the polymer, and soforth. For example, the loss tangent tan δ can be increased byincreasing the proportional content of aromatic vinyl monomer units inthe polymer. Moreover, the loss tangent tan δ can be controlled byaltering additives compounded in production of the polymer, for example.

Note that a loss tangent tan δ of not less than 0.001 and not more than0.80 for the polymer is preferable from a viewpoint of improvingpressability of an obtained electrode. When an electrode has goodpressability, this more specifically means that the amount ofspring-back and rate of density change of the electrode after pressingare small, and that an electrode mixed material layer has excellentclose adherence and has a low tendency to peel from an electrodesubstrate after pressing of the electrode.

<<Loss Modulus G″ of Polymer>>

The loss modulus G″ of the polymer is required to be 1,600 kPa or less,and is preferably 1,000 kPa or less. When the loss modulus G″ is notmore than any of the upper limits set forth above, peel strength of anelectrode can be improved. Note that besides peel strength after aproduced electrode is exposed to high temperature (high-temperature peelstrength) such as previously described, the peel strength of anelectrode referred to here may be peel strength of a produced electrodebefore exposure to high temperature (i.e., peel strength of a producedelectrode in that state, which is also referred to below as “normal peelstrength”). When the loss modulus G″ of the polymer is not more than anyof the upper limits set forth above, it is possible to increase eitheror both of high-temperature peel strength and normal peel strengththrough balancing with other parameters such as the loss tangent tan δ.Note that the loss modulus G″ is normally 1 kPa or more, but is notspecifically limited thereto.

Moreover, a loss modulus G″ of 1,800 kPa or less is preferable from aviewpoint of improving pressability of an obtained electrode.

Note that the loss modulus G″ of the polymer can be adjusted based onthe chemical composition of the polymer, production conditions of thepolymer, and so forth. For example, the loss modulus G″ can be reducedby reducing the proportional content of aromatic vinyl monomer units inthe polymer. Moreover, the loss modulus G″ can be controlled by alteringadditives compounded in production of the polymer, for example.

<<Gel Content of Polymer>>

The gel content measured when the polymer is immersed in tetrahydrofuranis preferably not less than 35 mass % and not more than 60 mass %. Whenthe gel content of the polymer is within this range, it is possible tocontrol the initial viscosity of an obtained slurry composition towithin an appropriate range. Moreover, when the gel content of thepolymer is not less than the lower limit set forth above, thermalstability of the polymer increases, and high-temperature peel strengthof an obtained electrode can be increased. Note that the gel content ofthe polymer can be adjusted based on the chemical composition of thepolymer, production conditions of the polymer, and so forth. Forexample, the gel content of the polymer can be increased by raising thereaction temperature in a graft polymerization reaction, increasing theamount of initiator that is compounded, and so forth.

<<Chemical Composition of Polymer>>

The polymer is required to include an aromatic vinyl monomer unit, aconjugated diene monomer unit, and a hydrophilic monomer unit and mayoptionally include other monomer units that are copolymerizable withthese monomer units. Moreover, from a viewpoint of enabling formation ofan electrode having even better high-temperature peel strength and evenfurther reducing internal resistance of an obtained secondary battery,it is preferable that the polymer includes an aromatic vinyl blockregion formed of aromatic vinyl monomer units. In other words, thepolymer is preferably a block copolymer that includes block regions.

[Aromatic Vinyl Monomer Unit]

Examples of aromatic vinyl monomers that can form an aromatic vinylmonomer unit include aromatic monovinyl compounds such as styrene,styrene sulfonic acid and salts thereof, a-methylstyrene,p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, andvinylnaphthalene. Of these aromatic vinyl monomers, styrene andderivatives thereof are preferable. Although one of these aromatic vinylmonomers may be used individually or two or more of these aromatic vinylmonomers may be used in combination, it is preferable that one aromaticvinyl monomer is used individually.

Aromatic vinyl monomer units of the polymer preferably constitute anaromatic vinyl block region formed of aromatic vinyl monomer units. Thearomatic vinyl block region is a region that only includes an aromaticvinyl monomer unit as a repeating unit. A single aromatic vinyl blockregion may be formed of just one type of aromatic vinyl monomer unit ormay be formed of a plurality of types of aromatic vinyl monomer units,but is preferably formed of just one type of aromatic vinyl monomerunit. Moreover, a single aromatic vinyl block region may include acoupling moiety (i.e., aromatic vinyl monomer units forming a singlearomatic vinyl block region may be linked via a coupling moiety). In acase in which the polymer includes a plurality of aromatic vinyl blockregions, the types and proportions of aromatic vinyl monomer unitsforming these aromatic vinyl block regions may be the same or differentfor each of the aromatic vinyl block regions, but are preferably thesame.

The proportion constituted by aromatic vinyl monomer units in thepolymer when the amount of all repeating units (monomer units andstructural units) in the polymer is taken to be 100 mass % is preferably10 mass % or more, and more preferably 15 mass % or more, and ispreferably 60 mass % or less, and more preferably 50 mass % or less.When the proportion constituted by aromatic vinyl monomer units in thepolymer is not less than any of the lower limits set forth above, cyclecharacteristics of a secondary battery can be improved. On the otherhand, when the proportion constituted by aromatic vinyl monomer units inthe polymer is not more than any of the upper limits set forth above,flexibility of the polymer is ensured, and peel strength of an electrodecan be further improved. Both high-temperature peel strength and normalpeel strength can be increased when the polymer has appropriateflexibility.

Note that in a case in which aromatic vinyl monomer units included inthe polymer form an aromatic vinyl block region, the proportionconstituted by aromatic vinyl monomer units in the polymer normallymatches the proportion constituted by the aromatic vinyl block region inthe polymer.

[Conjugated Diene Monomer Unit]

Examples of conjugated diene monomers that can form a conjugated dienemonomer unit include conjugated diene compounds having a carbon numberof 4 or more such as 1,3-butadiene, isoprene,2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. Of these conjugateddiene monomers, 1,3-butadiene and isoprene are preferable, and1,3-butadiene is more preferable. Although one of these conjugated dienemonomers may be used individually or two or more of these conjugateddiene monomers may be used in combination, it is preferable that oneconjugated diene monomer is used individually. This is becausedispersion stability and thermal stability of the obtained polymer canbe increased by using 1,3-butadiene to form a conjugated diene monomerunit of the polymer.

Conjugated diene monomer units of the polymer preferably constitute aconjugated diene block region formed of conjugated diene monomer units.The conjugated diene block region is a region that only includes aconjugated diene monomer unit as a repeating unit. A single conjugateddiene block region may be formed of just one type of conjugated dienemonomer unit or may be formed of a plurality of types of conjugateddiene monomer units, but is preferably formed of just one type ofconjugated diene monomer unit. Moreover, a single conjugated diene blockregion may include a coupling moiety (i.e., conjugated diene monomerunits forming a single conjugated diene block region may be linked via acoupling moiety). In a case in which the polymer includes a plurality ofconjugated diene block regions, the types and proportions of conjugateddiene monomer units forming these conjugated diene block regions may bethe same or different for each of the conjugated diene block regions,but are preferably the same.

The term “conjugated diene monomer unit” refers to a repeating unit thatis derived from a conjugated diene monomer, but may be inclusive ofeither or both of a unit that is formed of a polymerized conjugateddiene and a unit that is obtained through hydrogenation of a unit formedof a polymerized conjugated diene. The unit that is obtained throughhydrogenation of a unit formed of a polymerized conjugated diene may bean alkylene structural unit. An alkylene structural unit is a repeatingunit that is composed of only an alkylene structure represented by ageneral formula —C_(n)H_(2n)— (n is an integer of 2 or more). Althoughthe alkylene structural unit may be linear or branched, the alkylenestructural unit is preferably linear (i.e., is preferably a linearalkylene structural unit). Moreover, the carbon number of the alkylenestructural unit is preferably 4 or more (i.e., n in the precedinggeneral formula is preferably an integer of 4 or more). The method bywhich the alkylene structural unit is introduced into the polymer is notspecifically limited and may, for example, be a method involvinghydrogenating the polymer. Hydrogenation of the polymer can be performedby a commonly known method such as oil-layer hydrogenation orwater-layer hydrogenation.

The proportion constituted by conjugated diene monomer units in thepolymer when the amount of all repeating units (monomer units andstructural units) in the polymer is taken to be 100 mass % is preferably40 mass % or more, and more preferably 50 mass % or more, and ispreferably 80 mass % or less, and more preferably 75 mass % or less.When the proportion constituted by conjugated diene monomer units in thepolymer is not less than any of the lower limits set forth above,high-temperature peel strength and normal peel strength of an electrodecan both be even further improved. On the other hand, when theproportion constituted by conjugated diene monomer units in the polymeris not more than any of the upper limits set forth above, flexibility ofthe polymer is ensured, and cycle characteristics of a secondary batterycan be further improved. Note that in a case in which conjugated dienemonomer units included in the polymer form a conjugated diene blockregion, the proportion constituted by conjugated diene monomer units inthe polymer normally matches the proportion constituted by theconjugated diene block region in the polymer. Moreover, in a case inwhich the polymer includes an alkylene structural unit, the totalproportion constituted by alkylene structural units and non-hydrogenatedconjugated diene monomer units preferably satisfies any of the preferredranges set forth above.

[Hydrophilic Monomer Unit]

Examples of hydrophilic monomers that can form a hydrophilic monomerunit include, but are not specifically limited to, carboxylgroup-containing monomers, sulfo group-containing monomers, phosphategroup-containing monomers, hydroxy group-containing monomers, andreactive emulsifiers.

Examples of carboxyl group-containing monomers include monocarboxylicacids, derivatives of monocarboxylic acids, dicarboxylic acids, acidanhydrides of dicarboxylic acids, and derivatives of dicarboxylic acidsand acid anhydrides thereof.

Examples of monocarboxylic acids include acrylic acid, methacrylic acid,and crotonic acid.

Examples of derivatives of monocarboxylic acids include 2-ethylacrylicacid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylicacid, and α-chloro-β-E-methoxyacrylic acid.

Examples of dicarboxylic acids include maleic acid, fumaric acid, anditaconic acid.

Examples of derivatives of dicarboxylic acids include methylmaleic acid,dimethylmaleic acid, phenylmaleic acid, chloromaleic acid,dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters suchas butyl maleate, nonyl maleate, decyl maleate, dodecyl maleate,octadecyl maleate, and fluoroalkyl maleates.

Examples of acid anhydrides of dicarboxylic acids include maleicanhydride, acrylic anhydride, methylmaleic anhydride, dimethylmaleicanhydride, and citraconic anhydride.

Moreover, an acid anhydride that produces a carboxyl group throughhydrolysis can also be used as a carboxyl group-containing monomer.

Furthermore, an ethylenically unsaturated polybasic carboxylic acid suchas butene tricarboxylic acid, a partial ester of an ethylenicallyunsaturated polybasic carboxylic acid such as monobutyl fumarate ormono-2-hydroxypropyl maleate, or the like can be used as a carboxylgroup-containing monomer.

Examples of sulfo group-containing monomers include styrene sulfonicacid, vinyl sulfonic acid (ethylene sulfonic acid), methyl vinylsulfonic acid, (meth)allyl sulfonic acid, and3-allyloxy-2-hydroxypropane sulfonic acid.

In the present disclosure, “(meth)allyl” is used to indicate “allyl”and/or “methallyl”.

Examples of phosphate group-containing monomers include2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethylphosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

In the present disclosure, “(meth)acryloyl” is used to indicate“acryloyl” and/or “methacryloyl”.

Examples of hydroxy group-containing monomers include acrylic acidesters having a hydroxy group in a molecule thereof such as2-hydroxyethyl acrylate and methacrylic acid esters having a hydroxygroup in a molecule thereof such as 2-hydroxyethyl methacrylate.

Examples of reactive emulsifiers include emulsifiers based onpolyalkylene oxide that have an anionic functional group and/or anon-ionic functional group. For example, sodium styrenesulfonate, sodiumallyl alkyl sulfonate, alkyl allyl sulfosuccinate salt, polyoxyethylenealkyl allyl glycerin ether sulfate, polyoxyethylene alkylphenol allylglycerin ether sulfate, or the like may be used.

One of the hydrophilic monomers described above may be usedindividually, or two or more of the hydrophilic monomers described abovemay be used in combination. Acidic group-containing monomers such ascarboxyl group-containing monomers, sulfo group-containing monomers, andphosphate group-containing monomers are preferable as hydrophilicmonomers, and, particularly from a viewpoint of even further increasinghigh-temperature peel strength, carboxyl group-containing monomers aremore preferable, acrylic acid and methacrylic acid are even morepreferable, and methacrylic acid is particularly preferable.

Moreover, with regards to hydrophilic monomer units that can be formedusing the hydrophilic monomers described above, it is preferable that atleast some of these monomer units are present in the form of an alkalimetal salt of sodium, potassium, or the like or an ammonium salt in thepolymer. In particular, it is preferable that at least some hydrophilicmonomer units are present as an ammonium salt. When at least somehydrophilic monomer units are present as an ammonium salt, preservationstability of an obtained slurry composition can be even furtherincreased.

Hydrophilic monomer units may be intermingled with the above-describedaromatic vinyl monomer units and conjugated diene monomer units such asto form a random copolymer or may bonded as a graft chain to a coreparticle that is a block copolymer or random copolymer formed ofaromatic vinyl monomer units and conjugated diene monomer units. Inparticular, the polymer that is an essential component of the presentlydisclosed binder composition is preferably a polymer having a graftchain with a hydrophilic monomer unit as a repeating unit bonded to acore particle that is a block copolymer formed of an aromatic vinylblock region and a conjugated diene block region. Note that the blockcopolymer constituting the core particle preferably only includes anaromatic vinyl block region and a conjugated diene block region.

The proportion constituted by hydrophilic monomer units in the polymerwhen the amount of all repeating units (monomer units and structuralunits) in the polymer is taken to be 100 mass % is required to be notless than 4.0 mass % and not more than 20 mass %. Moreover, theproportion constituted by hydrophilic monomer units in the polymer ispreferably 5.0 mass % or more, and more preferably 5.5 mass % or more,and is preferably 16 mass % or less, and more preferably 10 mass % orless. When the proportion constituted by hydrophilic monomer units inthe polymer is not less than any of the lower limits set forth above,stability when a slurry composition is produced can be improved whilealso improving high-temperature peel strength and normal peel strengthof an obtained electrode. On the other hand, when the proportionconstituted by hydrophilic monomer units in the block copolymer is notmore than any of the upper limits set forth above, initial viscositywhen a slurry composition is produced can be restricted from becomingexcessively high, and, as a result, high-temperature peel strength andnormal peel strength of an obtained electrode can be improved.

Note that from a viewpoint of improving pressability of an obtainedelectrode, it is preferable that the proportion constituted byhydrophilic monomer units in the polymer is not less than 3.7 mass % andnot more than 20 mass % when the amount of all repeating units (monomerunits and structural units) in the polymer is taken to be 100 mass %.

[Other Monomer Units]

Examples of monomers that can form other monomer units that mayoptionally be included in the polymer include, but are not specificallylimited to, nitrile group-containing monomers such as acrylonitrile andmethacrylonitrile; and amide group-containing monomers.

<<Production Method of Polymer>>

In a case in which the entire polymer or core particles of the polymerare a random polymer, the polymer can be polymerized by any knownpolymerization method such as solution polymerization, suspensionpolymerization, bulk polymerization, or emulsion polymerization, forexample. Moreover, the polymerization reaction may be additionpolymerization such as ionic polymerization, radical polymerization, orliving radical polymerization. An emulsifier, dispersant, polymerizationinitiator, polymerization aid, or the like used in polymerization may bethe same as typically used and the amount thereof may also be the sameas typically used.

In a case in which core particles of the polymer are a block copolymer,the core particles can be produced, for example, through a step of blockpolymerizing an aromatic vinyl monomer and a conjugated diene monomersuch as described above in an organic solvent to obtain a solution of ablock copolymer including an aromatic vinyl block region and aconjugated diene block region (block copolymer solution production step)and a step of adding water to the obtained solution of the blockcopolymer and performing emulsification to form particles of the blockcopolymer (emulsification step).

—Block Copolymer Solution Production Step—

No specific limitations are placed on the method of block polymerizationin the block copolymer solution production step. For example, a blockcopolymer can be produced by adding a second monomer component to asolution obtained through polymerization of a first monomer componentdiffering from the second monomer component, polymerizing the secondmonomer component, and further repeating addition and polymerization ofmonomer components as necessary. The organic solvent that is used as areaction solvent is not specifically limited and can be selected asappropriate depending on the types of monomers and so forth.

A block copolymer obtained through block polymerization in this manneris preferably subjected to a coupling reaction using a coupling agent inadvance of the subsequently described emulsification step.

Examples of coupling agents that can be used in the coupling reactioninclude, but are not specifically limited to, difunctional couplingagents, trifunctional coupling agents, tetrafunctional coupling agents,and coupling agents having a functionality of 5 or higher.

Examples of difunctional coupling agents include difunctionalhalosilanes such as dichlorosilane, monomethyldichlorosilane, anddichlorodimethylsilane; difunctional haloalkanes such as dichloroethane,dibromoethane, methylene chloride, and dibromomethane; and difunctionaltin halides such as tin dichloride, monomethyltin dichloride,dimethyltin dichloride, monoethyltin dichloride, diethyltin dichloride,monobutyltin dichloride, and dibutyltin dichloride.

Examples of trifunctional coupling agents include trifunctionalhaloalkanes such as trichloroethane and trichloropropane; trifunctionalhalosilanes such as methyltrichlorosilane and ethyltrichlorosilane; andtrifunctional alkoxysilanes such as methyltrimethoxysilane,phenyltrimethoxysilane, and phenyltriethoxysilane.

Examples of tetrafunctional coupling agents include tetrafunctionalhaloalkanes such as carbon tetrachloride, carbon tetrabromide, andtetrachloroethane; tetrafunctional halosilanes such as tetrachlorosilaneand tetrabromosilane; tetrafunctional alkoxysilanes such astetramethoxysilane and tetraethoxysilane; and tetrafunctional tinhalides such as tin tetrachloride and tin tetrabromide.

Examples of coupling agents having a functionality of 5 or higherinclude 1,1,1,2,2 -pentachloroethane, perchloroethane,pentachlorobenzene, perchlorobenzene, octabromodiphenyl ether, anddecabromodiphenyl ether.

One of these coupling agents may be used individually, or two or more ofthese coupling agents may be used in combination.

Of the examples given above, dichlorodimethylsilane is preferable as thecoupling agent. The coupling reaction using the coupling agent resultsin a coupling moiety that is derived from the coupling agent beingintroduced into a constituent macromolecule chain (for example, atriblock structure) of the block copolymer.

Note that the block copolymer solution that is obtained after the blockpolymerization and optional coupling reaction described above may besubjected to the subsequently described emulsification step in that formor may be subjected to the emulsification step after addition of anadditive such as an antioxidant, as necessary. Moreover, the blockcopolymer may be caused to precipitate to obtain a dried product, theobtained dried product may be dissolved in a good solvent such ascyclohexane to obtain a block copolymer solution, and then this blockcopolymer solution may be subjected to the emulsification step.

—Emulsification Step—

Although no specific limitations are placed on the method ofemulsification in the emulsification step, a method in whichphase-inversion emulsification is performed with respect to apreliminary mixture of the block copolymer solution obtained in theblock copolymer solution production step described above and an aqueoussolution of an emulsifier is preferable, for example. Note that thephase-inversion emulsification can be carried out using a knownemulsifier and emulsifying/dispersing device, for example. Specificexamples of emulsifying/dispersing devices that can be used include, butare not specifically limited to, batch emulsifying/dispersing devicessuch as a Homogenizer (product name; produced by IKA), a Polytron(product name; produced by Kinematica AG), and a TK Auto Homo Mixer(product name; produced by Tokushu Kika Kogyo Co., Ltd.); continuousemulsifying/dispersing devices such as a TK Pipeline-Homo Mixer (productname; produced by Tokushu Kika Kogyo Co., Ltd.), a Colloid Mill (productname; produced by Shinko Pantec Co., Ltd.), a Thrasher (product name;produced by Nippon Coke & Engineering Co., Ltd.), a Trigonal Wet FineGrinding Mill (product name; produced by Mitsui Miike ChemicalEngineering Machinery Co., Ltd.), a Cavitron (product name; produced byEUROTEC Ltd.), a Milder (product name; produced by Pacific Machinery &Engineering Co., Ltd.), and a Fine Flow Mill (product name; produced byPacific Machinery & Engineering Co., Ltd.); high-pressureemulsifying/dispersing devices such as a Microfluidizer (product name;produced by Mizuho Industrial Co., Ltd.), a Nanomizer (product name;produced by Nanomizer Inc.), an APV Gaulin or LAB1000 (product name;produced by SPX FLOW, Inc.), a Star Burst (product name; produced bySugino Machine Limited), and an ECONIZER (product name; produced bySanmaru Machinery Co., Ltd.); membrane emulsifying/dispersing devicessuch as a Membrane Emulsifier (product name; produced by Reica Co.,Ltd.); vibratory emulsifying/dispersing devices such as a Vibro Mixer(product name; produced by Reica Co., Ltd.); and ultrasonicemulsifying/dispersing devices such as an Ultrasonic Homogenizer(product name; produced by Branson). Note that the conditions (forexample, treatment temperature, treatment time, etc.) of theemulsification operation by the emulsifying/dispersing device may beselected as appropriate to obtain the desired dispersion state withoutany specific limitations.

A known method may be used to remove organic solvent from the emulsionobtained after emulsification as necessary, for example, so as to yielda water dispersion of core particles containing the block copolymer.

By subjecting the core particles (random polymer or block copolymer)obtained through these steps to graft chain bonding (grafting step), itis possible to produce a graft polymer having a graft chain with ahydrophilic monomer unit as a repeating unit bonded to a core particle.

—Grafting Step—

Graft polymerization of a graft chain having a hydrophilic monomer unitas a repeating unit can be performed by a known graft polymerizationmethod without any specific limitations. More specifically, the graftpolymerization can be performed using a radical initiator such as aredox initiator that is a combination of an oxidant and a reductant, forexample. Known oxidants and reductants can be used as the oxidant andthe reductant without any specific limitations. Moreover, an alkalimetal salt of sodium, potassium, or the like or an ammonium salt may beused as a neutralizer after the graft polymerization has been stopped.In particular, it is preferable to use an ammonium salt as a neutralizerfrom a viewpoint of increasing preservation stability of an obtainedslurry composition. These neutralizers can be added to the graftpolymerization reaction liquid in the form of an aqueous solution, forexample.

In a case in which a redox initiator is used to perform graftpolymerization with respect to core particles that are a block copolymerincluding an aromatic vinyl block region and a conjugated diene blockregion, cross-linking of conjugated diene units in the block copolymermay be caused to occur during introduction of a hydrophilic graft chainby graft polymerization. Note that it is not essential thatcross-linking is caused to proceed concurrently to graft polymerizationin production of a graft polymer, and the type of radical initiatorand/or reaction conditions may be adjusted such that only graftpolymerization is caused to proceed.

By performing a graft polymerization reaction of a hydrophilic monomerwith respect to the core particles described above, it is possible toobtain the polymer as a graft polymer having a hydrophilic graft chainformed through repetition of a hydrophilic monomer unit bonded to a coreparticle.

<Solvent>

The presently disclosed binder composition is required to contain wateras a solvent, but may contain a small amount of an organic solvent inaddition to water.

<Other Components>

The presently disclosed binder composition can contain components otherthan those described above (i.e., other components). For example, thebinder composition may contain a known binder (styrene-butadiene randomcopolymer and/or acrylic polymer, etc.) other than the polymer describedabove.

Note that in a case in which the binder composition contains a binderother than the polymer described above, the content of the polymerdescribed above is preferably 50 mass % or more, more preferably 55 mass% or more, and even more preferably 60 mass % or more of the totalcontent of the polymer and the binder, and is preferably 90 mass % orless, more preferably 85 mass % or less, and even more preferably 80mass % or less of the total content of the polymer and the binder.

The binder composition may also contain a water-soluble polymer. Thewater-soluble polymer is a component that can cause good dispersion ofcomponents such as the above-described polymer in water, and ispreferably a synthetic polymer, and more preferably an addition polymerproduced by addition polymerization, but is not specifically limitedthereto. Note that the water-soluble polymer may be in the form of asalt (salt of water-soluble polymer). In other words, the term“water-soluble polymer” as used in the present disclosure is alsoinclusive of a salt of that water-soluble polymer. Also note that when apolymer is referred to as “water-soluble” in the present disclosure,this means that when 0.5 g of the polymer is dissolved in 100 g of waterat a temperature of 25° C., insoluble content is less than 1.0 mass %.

The binder composition may also contain known additives. Examples ofsuch known additives include antioxidants such as2,6-di-tert-butyl-p-cresol, defoamers, and dispersants (excluding thosecorresponding to the above-described water-soluble polymer).

One of these other components may be used individually, or two or moreof these other components may be used in combination in a freelyselected ratio.

<Production Method of Binder Composition>

The presently disclosed binder composition can be produced by mixing thepolymer, other optionally used components, and so forth in the presenceof water without any specific limitations. Note that in a situation inwhich a water dispersion of the polymer is used to produce the bindercomposition, liquid contained in this dispersion liquid may be used inthat form as a medium of the binder composition.

Slurry Composition for Non-Aqueous Secondary Battery Electrode

The presently disclosed slurry composition is a composition that is foruse in formation of an electrode mixed material layer of an electrode.The presently disclosed slurry composition contains the bindercomposition set forth above and further contains an electrode activematerial. In other words, the presently disclosed slurry compositioncontains the previously described polymer, an electrode active material,and water, and can further contain other optional components. As aresult of the presently disclosed slurry composition containing thebinder composition set forth above, an electrode that includes anelectrode mixed material layer formed from this slurry composition hasexcellent peel strength after exposure to high temperature. Moreover, asecondary battery that includes this electrode has low internalresistance.

<Binder Composition>

The binder composition is the presently disclosed binder composition setforth above that contains a specific polymer and water.

No specific limitations are placed on the amount of the bindercomposition in the slurry composition. For example, the amount of thebinder composition can be set as an amount such that, in terms of solidcontent, the amount of the polymer is not less than 0.5 parts by massand not more than 15 parts by mass per 100 parts by mass of theelectrode active material.

<Electrode Active Material>

Any known electrode active material that is used in secondary batteriescan be used as the electrode active material without any specificlimitations. Specifically, examples of electrode active materials thatcan be used in an electrode mixed material layer of a lithium ionsecondary battery, which is one example of a secondary battery, includethe following electrode active materials, but are not specificallylimited thereto.

[Positive Electrode Active Material]

A positive electrode active material that is compounded in a positiveelectrode mixed material layer of a positive electrode in a lithium ionsecondary battery may, for example, be a compound that includes atransition metal such as a transition metal oxide, a transition metalsulfide, or a complex metal oxide of lithium and a transition metal.Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu,and Mo.

Specific examples of positive electrode active materials that may beused include, but are not specifically limited to, lithium-containingcobalt oxide (LiCoO₂), lithium manganate (LiMn₂O₄), lithium-containingnickel oxide (LiNiO₂), a lithium-containing complex oxide of Co—Ni—Mnsuch as LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂ (NMC532), a lithium-containingcomplex oxide of Ni—Mn—Al, a lithium-containing complex oxide ofNi—Co—Al, olivine-type lithium iron phosphate (LiFePO₄), olivine-typelithium manganese phosphate (LiMnPO₄), a lithium-rich spinel compoundrepresented by Li_(1+x)Mn_(2-x)O₄ (0<x<2),Li[Ni_(0.17)Li_(0.2)Co_(0.07)Mn_(0.56)]O₂, and LiNi_(0.5)Mn_(1.5)O₄.

Note that one of the positive electrode active materials described abovemay be used individually, or two or more of the positive electrodeactive materials described above may be used in combination.

[Negative Electrode Active Material]

A negative electrode active material that is compounded in a negativeelectrode mixed material layer of a negative electrode in a lithium ionsecondary battery may, for example, be a carbon-based negative electrodeactive material, a metal-based negative electrode active material, or anegative electrode active material that is a combination thereof.

A carbon-based negative electrode active material can be defined as anactive material that contains carbon as its main framework and intowhich lithium can be inserted (also referred to as “doping”). Specificexamples of carbon-based negative electrode active materials includecarbonaceous materials such as coke, mesocarbon microbeads (MCMB),mesophase pitch-based carbon fiber, pyrolytic vapor-grown carbon fiber,pyrolyzed phenolic resin, polyacrylonitrile-based carbon fiber,quasi-isotropic carbon, pyrolyzed furfuryl alcohol resin (PFA), and hardcarbon; and graphitic materials such as natural graphite and artificialgraphite.

A metal-based negative electrode active material is an active materialthat contains metal, the structure of which usually contains an elementthat allows insertion of lithium, and that has a theoretical electriccapacity per unit mass of 500 mAh/g or more when lithium is inserted.Examples of metal-based active materials include lithium metal; a simplesubstance of metal that can form a lithium alloy (for example, Ag, Al,Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, or Ti); and anoxide, sulfide, nitride, silicide, carbide, or phosphide of any of thepreceding examples. Moreover, an oxide such as lithium titanate can beused.

Note that one of the negative electrode active materials described abovemay be used individually, or two or more of the negative electrodeactive materials described above may be used in combination.

<Other Components>

Examples of other components that can be contained in the slurrycomposition include, but are not specifically limited to, conductivematerials and the same components as other components that can becontained in the presently disclosed binder composition. Note that oneother component may be used individually, or two or more othercomponents may be used in combination in a freely selected ratio.

<Production of Slurry Composition>

No specific limitations are placed on the method by which the slurrycomposition is produced.

For example, the slurry composition can be produced by mixing the bindercomposition, the electrode active material, and other components thatare used as necessary in the presence of water.

Note that a medium used in production of the slurry composition mayinclude a medium that was contained in the binder composition. Themixing method is not specifically limited and can be mixing using atypically used stirrer or disperser.

Electrode for Non-Aqueous Secondary Battery

The presently disclosed electrode for a non-aqueous secondary batteryincludes an electrode mixed material layer formed using the slurrycomposition for a non-aqueous secondary battery electrode set forthabove. Consequently, the electrode mixed material layer is formed of adried product of the slurry composition set forth above, normallycontains the electrode active material and a component derived from thepolymer, and optionally contains other components. It should be notedthat components contained in the electrode mixed material layer arecomponents that were contained in the slurry composition for anon-aqueous secondary battery electrode. Furthermore, the preferredratio of these components in the electrode mixed material layer is thesame as the preferred ratio of these components in the slurrycomposition. Although the polymer is present in a particulate form inthe binder composition and the slurry composition, the polymer may havea particulate form or any other form in the electrode mixed materiallayer formed using the slurry composition.

The presently disclosed electrode for a non-aqueous secondary batteryhas excellent peel strength after exposure to high temperature as aresult of the electrode mixed material layer being formed using theslurry composition for a non-aqueous secondary battery electrode setforth above. Moreover, a secondary battery that includes the electrodehas low internal resistance.

<Production of Electrode for Non-Aqueous Secondary Battery>

The electrode mixed material layer of the presently disclosed electrodefor a non-aqueous secondary battery can be formed by any of thefollowing methods, for example.

-   -   (1) A method in which the presently disclosed slurry composition        is applied onto the surface of a current collector and is then        dried    -   (2) A method in which a current collector is immersed in the        presently disclosed slurry composition and is then dried    -   (3) A method in which the presently disclosed slurry composition        is applied onto a releasable substrate and is dried to produce        an electrode mixed material layer that is then transferred onto        the surface of a current collector

Of these methods, method (1) is particularly preferable since it allowssimple control of the thickness of the electrode mixed material layer.In more detail, method (1) includes a step of applying the slurrycomposition onto a current collector (application step) and a step ofdrying the slurry composition that has been applied onto the currentcollector to form an electrode mixed material layer on the currentcollector (drying step).

[Application Step]

The slurry composition can be applied onto the current collector by anycommonly known method without any specific limitations. Specificexamples of application methods that can be used include doctor blading,dip coating, reverse roll coating, direct roll coating, gravure coating,extrusion coating, and brush coating. During application, the slurrycomposition may be applied onto one side or both sides of the currentcollector. The thickness of the slurry coating on the current collectorafter application but before drying may be set as appropriate inaccordance with the thickness of the electrode mixed material layer tobe obtained after drying.

The current collector onto which the slurry composition is applied is amaterial having electrical conductivity and electrochemical durability.Specifically, the current collector may, for example, be made of iron,copper, aluminum, nickel, stainless steel, titanium, tantalum, gold,platinum, or the like. One of these materials may be used individually,or two or more of these materials may be used in combination in a freelyselected ratio.

[Drying Step]

The slurry composition on the current collector can be dried by anycommonly known method without any specific limitations. Examples ofdrying methods that can be used include drying by warm, hot, orlow-humidity air; drying in a vacuum; and drying by irradiation withinfrared light, electron beams, or the like. Through drying of theslurry composition on the current collector as described above, anelectrode mixed material layer is formed on the current collector,thereby providing an electrode for a non-aqueous secondary battery thatincludes the current collector and the electrode mixed material layer.

After the drying step, the electrode mixed material layer may be furthersubjected to a pressing process, such as mold pressing or roll pressing.The pressing process improves close adherence of the electrode mixedmaterial layer and the current collector and enables furtherdensification of the obtained electrode mixed material layer.Furthermore, in a case in which the electrode mixed material layercontains a curable polymer, the polymer is preferably cured after theelectrode mixed material layer has been formed.

Non-Aqueous Secondary Battery

The presently disclosed non-aqueous secondary battery includes apositive electrode, a negative electrode, an electrolyte solution, and aseparator, and has the electrode for a non-aqueous secondary battery setforth above as at least one of the positive electrode and the negativeelectrode. The presently disclosed non-aqueous secondary battery candisplay excellent cycle characteristics as a result of being produced byusing the electrode for a non-aqueous secondary battery set forth aboveas at least one of the positive electrode and the negative electrode.

Although the following describes, as one example, a case in which thesecondary battery is a lithium ion secondary battery, the presentlydisclosed secondary battery is not limited to the following example.

<Electrodes>

Examples of electrodes other than the presently disclosed electrode fora non-aqueous secondary battery set forth above that can be used in thepresently disclosed non-aqueous secondary battery include knownelectrodes that are used in production of secondary batteries withoutany specific limitations. Specifically, an electrode obtained by formingan electrode mixed material layer on a current collector by a knownproduction method may be used as an electrode other than the presentlydisclosed electrode for a non-aqueous secondary battery set forth above.

<Electrolyte Solution>

The electrolyte solution is normally an organic electrolyte solutionobtained by dissolving a supporting electrolyte in an organic solvent.The supporting electrolyte of the lithium ion secondary battery may, forexample, be a lithium salt. Examples of lithium salts that can be usedinclude LiPF₆, LiAsF₆, LiBF₄, LiSbF₆, LiAlCl₄, LiClO₄, CF₃SO₃Li,C₄F₉SO₃Li, CF₃COOLi, (CF₃CO)₂NLi, (CF₃SO₂)₂NLi, and (C₂F₅SO₂)NLi. Ofthese lithium salts, LiPF₆, LiClO₄, and CF₃SO₃Li are preferable as theyreadily dissolve in solvents and exhibit a high degree of dissociation.One electrolyte may be used individually, or two or more electrolytesmay be used in combination in a freely selected ratio. In general,lithium ion conductivity tends to increase when a supporting electrolytehaving a high degree of dissociation is used. Therefore, lithium ionconductivity can be adjusted through the type of supporting electrolytethat is used.

No specific limitations are placed on the organic solvent used in theelectrolyte solution so long as the supporting electrolyte can dissolvetherein. Examples of organic solvents that can suitably be used includecarbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC),diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate(BC), ethyl methyl carbonate (EMC), and vinylene carbonate (VC); esterssuch as γ-butyrolactone and methyl formate; ethers such as1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compoundssuch as sulfolane and dimethyl sulfoxide. Furthermore, a mixture of suchsolvents may be used. Of these solvents, carbonates are preferable dueto having high permittivity and a wide stable potential region. Ingeneral, lithium ion conductivity tends to increase when a solventhaving a low viscosity is used. Therefore, lithium ion conductivity canbe adjusted through the type of solvent that is used.

The concentration of the electrolyte in the electrolyte solution may beadjusted as appropriate. Furthermore, known additives may be added tothe electrolyte solution.

<Separator>

Examples of separators that can be used include, but are notspecifically limited to, those described in JP2012-204303A. Of theseseparators, a microporous membrane made of polyolefinic (polyethylene,polypropylene, polybutene, or polyvinyl chloride) resin is preferredbecause such a membrane can reduce the total thickness of the separator,which increases the ratio of electrode active material in the secondarybattery, and consequently increases the volumetric capacity.

The presently disclosed secondary battery can be produced by, forexample, stacking the positive electrode and the negative electrode withthe separator in-between, performing rolling, folding, or the like ofthe resultant laminate, as necessary, in accordance with the batteryshape, placing the laminate in a battery container, injecting theelectrolyte solution into the battery container, and sealing the batterycontainer. The electrode for a non-aqueous secondary battery set forthabove is used as at least one of the positive electrode and the negativeelectrode in the presently disclosed non-aqueous secondary battery, andis preferably used as the negative electrode. Note that the presentlydisclosed non-aqueous secondary battery may be provided with anovercurrent preventing device such as a fuse or a PTC device; anexpanded metal; or a lead plate, as necessary, in order to preventpressure increase inside the secondary battery and occurrence ofovercharging or overdischarging. The shape of the secondary battery maybe a coin type, button type, sheet type, cylinder type, prismatic type,flat type, or the like.

EXAMPLES

The following provides a more specific description of the presentdisclosure based on examples. However, the present disclosure is notlimited to the following examples. In the following description, “%” and“parts” used in expressing quantities are by mass, unless otherwisespecified.

Moreover, in the case of a polymer that is produced throughpolymerization of a plurality of types of monomers, the proportion inthe polymer constituted by a monomer unit that is formed throughpolymerization of a given monomer is normally, unless otherwisespecified, the same as the ratio (charging ratio) of the given monomeramong all monomers used in polymerization of the polymer.

In the examples and comparative examples, various attributes andevaluations were measured or performed as described below.

Proportional Contents of Monomer Units in Polymer

The proportional contents of monomer units in a polymer produced in eachexample or comparative example were measured by ¹H-NMR (produced by JEOLLtd.). Specifically, the peak area attributed to each monomer wasdetermined, this peak area was divided by the number of protons includedin the peak to calculate the molar ratio of monomer units, and then thiswas converted to a weight ratio using the molecular weight of eachmonomer.

Median Diameter of Polymer

The median diameter of a polymer was measured using a laser diffractionparticle diameter distribution analyzer (produced by

Shimadzu Corporation; product name: SALD-2300). Specifically, a waterdispersion of the polymer was prepared, a particle size distribution (byvolume) was measured using the above-described device, and the particlediameter at which cumulative volume calculated from a small diameter endof the distribution reached 50% was determined as the median diameter(μm).

Gel Content of Polymer

A binder composition produced in each example or comparative example wasdried at 50% humidity and room temperature (23° C. to 25° C.) to form afilm of approximately 0.3 mm in thickness. The formed film was cut to 3mm-square and was precisely weighed. The mass of the film piece obtainedby this cutting was taken to be w0. The film piece was immersed in 100 gof tetrahydrofuran (THF) at 25° C. for 24 hours. Thereafter, the filmpiece was pulled out of the THF, was vacuum dried at 105° C. for 3hours, and then the mass w1 of insoluble content was measured. The gelcontent (mass %) of the polymer was calculated according to thefollowing formula.

Gel content(mass%)=(w1/w0)×100

Loss Tangent tan δ and Loss Modulus G″ of Polymer

<<Production of Polymer Film>>

A binder composition produced in each example or comparative example wasmeasured out onto a Teflon® (Teflon is a registered trademark in Japan,other countries, or both) petri dish such as to have a thickness afterdrying of 50 μm. Thereafter, 12 hours of vacuum drying was performed atroom temperature to obtain a polymer film.

<<Measurement of Viscoelasticity of Polymer Film>>

The polymer film produced as described above was used in measurement bya viscoelasticity measurement device (Production RPA produced by AlphaTechnologies) while increasing the temperature in stages from 30° C. to200° C. under conditions of a frequency of 52 Hz and a strain of 10%. Inthis measurement, the loss modulus G″ and the loss tangent tan δ werecalculated based on results at 30° C.

Stationary Stability of Binder Composition

A test tube of 10 cm in length was prepared. A binder compositionproduced in each example or comparative example was poured into the testtube up to a height of 5 mm from the top thereof, and then a lid wasplaced on the test tube to obtain a test sample. This test sample wasstored at rest in an environment having a temperature of 25° C. for 1month. The test tube was subsequently unsealed, and 1 g of bindercomposition was sampled from each of an upper layer portion and a lowerlayer portion of the liquid. In this sampling, a Pasteur pipette wasused to perform sampling at a depth of 1 cm from the liquid surface forthe upper layer sample and at a height of 1 cm from the bottom surfacefor the lower layer sample. Each of these samples was subsequently driedon an aluminum plate, and the solid content concentration of each samplewas calculated from the weight change between before and after drying.The drying conditions were set as 30 minutes at 130° C., and the solidcontent concentration was determined based on the following formula.

Solid content concentration=(Weight after drying)/(Weight beforedrying)×100

-   -   A: Solid content concentration difference between upper layer        and lower layer portions of less than 1%    -   B: Solid content concentration difference between upper layer        and lower layer portions of not less than 1% and less than 2%    -   C: Solid content concentration difference between upper layer        and lower layer portions of not less than 2% and less than 3%    -   D: Solid content concentration difference between upper layer        and lower layer portions of 3% or more

Initial Viscosity of Slurry Composition

A planetary mixer was charged with 97.5 parts of natural graphite(theoretical capacity: 360 mAh/g) as a negative electrode activematerial and 1 part in terms of solid content of carboxymethyl celluloseas a thickener. These materials were diluted to a solid contentconcentration of 60% with deionized water and were then kneaded at arotation speed of 45 rpm for 60 minutes. Thereafter, 1.5 parts in termsof solid content of a binder composition for a negative electrodeobtained in each example was loaded into the planetary mixer, and afurther 40 minutes of kneading was performed at a rotation speed of 40rpm. The solid content was further adjusted to 48% with deionized water,and then the viscosity was measured using a B-type viscometer (producedby Toki Sangyo Co., Ltd.; product name: TVB-10; rotation speed: 60 rpm).

-   -   A: Less than 3,000 rpm    -   B: Not less than 3,000 rpm and less than 3,500 rpm    -   C: Not less than 3,500 rpm and less than 4,000 rpm    -   D: 4,000 rpm or more

Preservation Stability of Slurry Composition

The viscosity η0 of an obtained slurry composition was measured using aB-type viscometer (produced by Toki Sangyo Co., Ltd.; product name:TVB-10; rotation speed: 60 rpm). Next, the slurry composition that hadundergone viscosity measurement was stirred for 24 hours using aplanetary mixer (rotation speed: 60 rpm), and the viscosity η1 of theslurry composition after stirring was measured using the same type ofB-type viscometer as described above (rotation speed: 60 rpm). Theviscosity maintenance rate Δη of the slurry composition between beforeand after stirring was calculated (Δη=(η0−η1)/η0×100(%)), and thenviscosity stability of the slurry composition was evaluated by thefollowing standard. Note that the temperature during viscositymeasurement was 25° C. An absolute value |Δη| for the viscositymaintenance rate that is closer to 0 indicates that the slurrycomposition has better viscosity stability.

-   -   A: Absolute value |Δη| for viscosity maintenance rate of not        less than 0% and less than 10%    -   B: Absolute value |Δη| for viscosity maintenance rate of not        less than 10% and less than 20%    -   C: Absolute value |Δη| for viscosity maintenance rate of not        less than 20% and less than 30%    -   D: Absolute value |Δη≡ for viscosity maintenance rate of 30% or        more

Normal Peel Strength of Electrode

A negative electrode produced in each example or comparative examplewas, in that state, cut out as a rectangle of 100 mm in length and 10 mmin width to obtain a test specimen. The test specimen was placed withthe surface of the negative electrode mixed material layer facingdownward, and cellophane tape was affixed to the surface of the negativeelectrode mixed material layer. Cellophane tape prescribed by JIS Z1522was used as the cellophane tape. Moreover, the cellophane tape was fixedto a test stage. Thereafter, one end of the current collector was pulledvertically upward at a pulling speed of 50 mm/min to peel off thecurrent collector, and the stress during this peeling was measured.Three measurements were made in this manner. An average value of thesemeasurements was determined and was taken to be the peel strength. Alarger peel strength indicates greater binding strength of the negativeelectrode mixed material layer to the current collector (i.e., greaterclose adherence strength).

-   -   A: Peel strength of 16 N/m or more.    -   B: Peel strength of not less than 14 N/m and less than 16 N/m    -   C: Peel strength of not less than 12 N/m and less than 14 N/m    -   D: Peel strength of less than 12 N/m

High-Temperature Peel Strength of Electrode

A negative electrode produced in each example or comparative example wasvacuum dried at 100° C. for 10 hours and was then cut out as a rectangleof 100 mm in length and 10 mm in width to obtain a test specimen. Thetest specimen was placed with the surface of the negative electrodemixed material layer facing downward, and cellophane tape was affixed tothe surface of the negative electrode mixed material layer. Cellophanetape prescribed by JIS Z1522 was used as the cellophane tape. Moreover,the cellophane tape was fixed to a test stage. Thereafter, one end ofthe current collector was pulled vertically upward at a pulling speed of50 mm/min to peel off the current collector, and the stress during thispeeling was measured. Three measurements were made in this manner. Anaverage value of these measurements was determined and was taken to bethe peel strength. A larger peel strength as measured in this mannerindicates greater binding strength of the negative electrode mixedmaterial layer to the current collector after exposure to hightemperature (i.e., greater close adherence strength after exposure tohigh temperature).

-   -   A: Peel strength of 22 N/m or more    -   B: Peel strength of not less than 18 N/m and less than 22 N/m    -   C: Peel strength of not less than 14 N/m and less than 18 N/m    -   D: Peel strength of less than 14 N/m

Internal Resistance of Secondary Battery

IV resistance was measured as described below using a lithium ionsecondary battery prepared in each example or comparative example as ameasurement subject. The lithium ion secondary battery was subjected toconditioning by performing three cycles of an operation of charging to avoltage of 4.2 V with a charge rate of 0.1 C, resting for 10 minutes,and subsequently CV discharging to 3.0 V with a discharge rate of 0.1 Cat a temperature of 25° C. Thereafter, the lithium ion secondary batterywas charged to 3.75 V at 1 C (C is a value expressed by rated capacity(mA)/1 hour (hr)) and was subjected to 15 seconds of charging and 15seconds of discharging centered around 3.75 V at each of 0.5 C, 1.0 C,1.5 C, and 2.0 C in a −10° C. atmosphere. The battery voltage after 15seconds at the charging side in each case was plotted against thecurrent value, and the gradient of this plot was determined as thecharging IV resistance (Ω). The obtained IV resistance value (Ω) wasevaluated by the following standard. A smaller IV resistance valueindicates that the secondary battery has less internal resistance andbetter low-temperature characteristics.

-   -   A: IV resistance of 15 Ω or less    -   B: IV resistance of more than 15 Ω and not more than 17 Ω    -   C: IV resistance of more than 17 Ω

Close Adherence of Electrode Mixed Material Layer after Pressing

An edge of a negative electrode produced in each example or comparativeexample was visually inspected in order to confirm whether there was asite where the negative electrode mixed material layer and the currentcollector were peeled by 1 mm or more in an inward direction from theedge. In a case in which such a peeling site was not confirmed, thepost-pressing electrode mixed material layer was considered to have alow tendency to peel from a substrate, and an evaluation of “good” wasgiven.

Rate of Density Change of Electrode after Pressing

The density of an electrode mixed material layer in a negative electrodeproduced in each example or comparative example was remeasured after 24hours of storage in the same environment having a temperature of 25±3°C. In a case in which the reduction of density was 0.10 g/cm³ or less,the electrode was considered to have a low tendency for spring-back tooccur, and an evaluation of “good” was given.

Example 1

<Production of Binder Composition for Non-Aqueous Secondary BatteryNegative Electrode>

<<Production of Polymer>>

[Production of Cyclohexane Solution of Block Copolymer]

A pressure-resistant reactor was charged with 233.3 kg of cyclohexane,54.2 mmol of N,N,N′,N′-tetramethylethylenediamine (hereinafter, referredto as “TMEDA”), and 30.0 kg of styrene as an aromatic vinyl monomer.These materials were stirred at 40° C. while adding 1806.5 mmol ofn-butyllithium as a polymerization initiator, and then 1 hour ofpolymerization was performed while raising the temperature to 50° C. Thepolymerization conversion rate of styrene was 100%. Next, 70.0 kg ofbutadiene as an aliphatic conjugated diene monomer was continuouslyadded into the pressure-resistant reactor over 1 hour while performingtemperature control to maintain a temperature of 50° C. to 60° C. Thepolymerization reaction was continued for 1 hour more after addition ofthe butadiene was complete. The polymerization conversion rate ofbutadiene was 100%. Next, 722.6 mmol of dichlorodimethylsilane as acoupling agent was added into the pressure-resistant reactor and acoupling reaction was carried out for 2 hours to form astyrene-butadiene coupled block copolymer. Thereafter, 3612.9 mmol ofmethanol was added to the reaction liquid and was thoroughly mixedtherewith to deactivate active ends. Next, 0.3 parts of2,6-di-tert-butyl-p-cresol as an antioxidant was added to 100 parts ofthe reaction liquid (containing 30.0 parts of polymer component) and wasmixed therewith. The resultant mixed solution was gradually addeddropwise into hot water of 85° C. to 95° C. to cause volatilization ofsolvent and obtain a precipitate. The precipitate was pulverized andthen hot-air dried at 85° C. to collect a dried product containing ablock copolymer.

The collected dried product was dissolved in cyclohexane to produce ablock copolymer solution having a block copolymer concentration of 15%.

[Phase-Inversion Emulsification]

Sodium alkylbenzene sulfonate was dissolved in deionized water toproduce a 5% aqueous solution. After loading 5,000 g of the obtainedblock copolymer solution and 5,000 g of the obtained aqueous solutioninto a tank, preliminary mixing thereof was performed by stirring. Next,the preliminary mixture was transferred from the tank to a continuoushigh performance emulsifying/dispersing device (produced by PacificMachinery & Engineering Co., Ltd.; product name: CAVITRON) at a rate of100 g/min using a metering pump and was stirred at a rotation speed of20,000 rpm so as to obtain an emulsion in which the preliminary mixturehad undergone phase-inversion emulsification.

Next, cyclohexane in the obtained emulsion was evaporated under reducedpressure in a rotary evaporator. The emulsion that had been subjected toevaporation was subsequently subjected to 10 minutes of centrifugationat 7,000 rpm in a centrifuge (produced by Hitachi Koki Co., Ltd.;product name: Himac CR21N), and then the upper layer portion waswithdrawn to perform concentrating.

Finally, the upper layer portion was filtered through a 100-mesh screento obtain a water dispersion containing a particulate block copolymer(block copolymer latex).

[Graft Polymerization and Cross-Linking]

Distilled water was added to dilute the obtained block copolymer latexsuch that the amount of water was 850 parts relative to 100 parts (interms of solid content) of the particulate block copolymer. The dilutedblock copolymer latex was loaded into a stirrer-equipped polymerizationreactor that had undergone nitrogen purging and was heated to atemperature of 30° C. under stirring. In addition, a separate vessel wasused to produce a diluted methacrylic acid solution by mixing 6 parts ofmethacrylic acid as a hydrophilic monomer and 15 parts of distilledwater. The diluted methacrylic acid solution was added over 30 minutesinto the polymerization reactor that had been heated to 30° C.

A separate vessel was used to produce a solution (g) containing 7 partsof distilled water and 0.6 parts of ascorbic acid as a reductant. Theobtained solution was added into the polymerization reactor, 0.5 partsof cumene hydroperoxide (produced by NOF Corporation; product name: CHP)was subsequently added as an oxidant, and a reaction was carried out at30° C. for 1 hour and then at 70° C. for 2 hours to yield a waterdispersion of a particulate polymer. The polymerization conversion ratewas 99%.

The obtained water dispersion was adjusted to pH 8 through addition of8% ammonia water.

<Production of Slurry Composition for Secondary Battery PositiveElectrode>

In a planetary mixer, 97 parts of an active material NMC532(LiNi_(5/10)Co_(2/10)Mn_(3/10)O₂) based on a lithium complex oxide ofCo—Ni—Mn as a positive electrode active material, 1 part of acetyleneblack (produced by Denka Company Limited; product name: HS-100) as aconductive material, 1 part in terms of solid content of the polymerobtained as described above, and 1 part of PVdF (KF7208 produced byKureha Corporation) were added together and mixed. In addition,N-methyl-2-pyrrolidone (NMP) was gradually added as an organic solventand was mixed therewith by stirring at a temperature of 25±3° C. and arotation speed of 25 rpm to adjust the viscosity (B-type viscometer; 60rpm (M4 rotor); 25±3° C.) to 3,600 mPa·s.

<Production of Positive Electrode>

The slurry composition for a positive electrode obtained as describedabove was applied onto aluminum foil of 20 μm in thickness serving as acurrent collector by a comma coater such as to have a coating weight of20±0.5 mg/cm².

The aluminum foil was then conveyed inside an oven having a temperatureof 120° C. for 2 minutes and an oven having a temperature of 130° C. for2 minutes at a speed of 200 mm/min so as to dry the slurry compositionon the aluminum foil and thereby obtain a positive electrode webincluding a positive electrode mixed material layer formed on thecurrent collector.

The positive electrode mixed material layer-side of the producedpositive electrode web was subsequently roll pressed in an environmenthaving a temperature of 25±3° C. to obtain a positive electrode having apositive electrode mixed material layer density of 3.20 g/cm³.

<Production of Slurry Composition for Negative Electrode>

A planetary mixer was charged with 97.5 parts of natural graphite(theoretical capacity: 360 mAh/g) as a negative electrode activematerial and 1 part in terms of solid content of carboxymethyl celluloseas a thickener. These materials were diluted to a solid contentconcentration of 60% with deionized water and were subsequently kneadedat a rotation speed of 45 rpm for 60 minutes. Thereafter, 1.5 parts interms of solid content of the binder composition for a negativeelectrode obtained as described above was loaded into the planetarymixer, and a further 40 minutes of kneading was performed at a rotationspeed of 40 rpm. In addition, deionized water was added to adjust theviscosity to 3,000±500 mPa·s (measured by B-type viscometer at 25° C.and 60 rpm) and thereby produce a slurry composition for a negativeelectrode.

<Production of Negative Electrode>

The slurry composition for a negative electrode was applied onto thesurface of electrolytic copper foil of 15 μm in thickness serving as acurrent collector by a comma coater such as to have a coating weight of11±0.5 mg/cm². The copper foil with the slurry composition for anegative electrode applied thereon was then conveyed inside an ovenhaving a temperature of 120° C. for 2 minutes and an oven having atemperature of 130° C. for 2 minutes at a speed of 400 mm/min so as todry the slurry composition on the copper foil and thereby obtain anegative electrode web including a negative electrode mixed materiallayer formed on the current collector.

The negative electrode mixed material layer-side of the producednegative electrode web was subsequently roll pressed in an environmenthaving a temperature of 25±3° C. to obtain a negative electrode having anegative electrode mixed material layer density of 1.60 g/cm³.

<Preparation of Separator for Secondary Battery>

A separator made of a single layer of polypropylene (#2500 produced byCelgard, LLC.) was used.

<Production of Non-Aqueous Secondary Battery>

The negative electrode, positive electrode, and separator describedabove were used to produce a single-layer laminate cell (initial designdischarge capacity equivalent to 30 mAh), were then arranged insidealuminum packing, and were subjected to vacuum drying under conditionsof 10 hours at 60° C. Thereafter, LiPF₆ solution of 1.0 M inconcentration (solvent: mixed solvent of ethylene carbonate (EC)/diethylcarbonate (DEC)=5/5 (volume ratio); additive: containing 2 volume %(solvent ratio) of vinylene carbonate) was loaded into the aluminumpacking as an electrolyte solution. The aluminum packing was then closedby heat sealing at a temperature of 150° C. to tightly seal an openingof the aluminum packing, and thereby produce a lithium ion secondarybattery. This lithium ion secondary battery was used to evaluateinternal resistance as previously described. The result is shown inTable 1.

Example 2

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, the amounts of styrene, 1,3-butadiene, and methacrylic acidwere changed such that the obtained polymer had a chemical compositionindicated in Table 1 and the concentration of the block copolymer addedin phase-inversion emulsification was changed so as to obtain a polymerhaving a particle diameter indicated in Table 1. The results are shownin Table 1.

Examples 3 and 4

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, the amounts of styrene and 1,3-butadiene were changed such thatthe obtained polymer had a chemical composition indicated in Table 1 andthe concentration of the block copolymer added in phase-inversionemulsification was changed so as to obtain a polymer having a particlediameter and film properties indicated in Table 1. The results are shownin Table 1.

Example 5

Various operations, measurements, and evaluations were performed in thesame way as in Example 2 with the exception that the concentration ofthe block copolymer added in phase-inversion emulsification in theprocess of producing the polymer was changed so as to obtain a polymerhaving a particle diameter and film properties indicated in Table 1. Theresults are shown in Table 1.

Examples 6 to 8

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, isoprene was used instead of 1,3-butadiene as a conjugateddiene monomer, the amounts of styrene and isoprene there were compoundedwere changed such that the obtained polymer had a chemical compositionindicated in Table 1, and the concentration of the block copolymer addedin phase-inversion emulsification was changed so as to obtain a polymerhaving a particle diameter and film properties indicated in Table 1. Theresults are shown in Table 1.

Example 9

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, the amounts of styrene, 1,3-butadiene, and methacrylic acidwere changed such that the obtained polymer had a chemical compositionindicated in Table 1 and the concentration of the block copolymer addedin phase-inversion emulsification was changed so as to obtain a polymerhaving a particle diameter and film properties indicated in Table 1. Theresults are shown in Table 1.

Example 10

Various operations, measurements, and evaluations were performed in thesame way as in Example 2 with the exception that the concentration ofthe block copolymer added in phase-inversion emulsification in theprocess of producing the polymer was changed so as to obtain a polymerhaving a particle diameter and film properties indicated in Table 1. Theresults are shown in Table 1.

Example 11

Various operations, measurements, and evaluations were performed in thesame way as in Example 2 with the exception that acrylic acid wascompounded instead of methacrylic acid as a hydrophilic monomer inproduction of the polymer. The results are shown in Table 1.

Example 12

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that the slurry compositionfor a negative electrode was produced using a random copolymer producedas described below as a polymer in addition to the block copolymerproduced in Example 1. Note that the mixing ratio of the block copolymerand the random copolymer in production of the slurry composition for anegative electrode was by mass. Also note that the chemical composition,median diameter, and film properties of a copolymer indicated in Table 1are for a mixture of the block copolymer and the random copolymer.

<Production of Random Copolymer>

With respect to a mixture of 62 parts of 1,3-butadiene as an aliphaticconjugated diene monomer, 34 parts of styrene as an aromatic vinylmonomer, 4 parts of methacrylic acid as a hydrophilic monomer, 0.3 partsof tert-dodecyl mercaptan as a chain transfer agent, 0.3 parts of sodiumlauryl sulfate as an emulsifier, and 150 parts of deionized water thatwas loaded into a vessel A, addition thereof into a pressure-resistantvessel B from the vessel A was initiated, and, simultaneously thereto,addition of 1 part of potassium persulfate as a polymerization initiatorinto the pressure-resistant vessel B was also initiated so as toinitiate polymerization. The reaction temperature was maintained at 75°C.

Once 5 hours 30 minutes had passed from the start of polymerization, thetemperature was raised to 85° C., and the reaction was continued for 6hours.

The reaction was quenched by cooling at the point at which thepolymerization conversion rate reached 97% to yield a mixture containinga particulate random polymer. The mixture containing the particulaterandom polymer was adjusted to pH 8 through addition of 5% sodiumhydroxide aqueous solution. Unreacted monomer was subsequently removedthrough thermal-vacuum distillation. Cooling was then performed to yielda water dispersion (solid content concentration: 40%) containing therandom polymer.

Example 13

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that sodium hydroxideaqueous solution was used for neutralization in the grafting step duringproduction of the polymer. The results are shown in Table 1.

Example 14

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that the slurry compositionfor a negative electrode was produced using only the random polymerproduced in Example 12 as a polymer. The results are shown in Table 1.

Comparative Example 1

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, the amounts of styrene, 1,3-butadiene, and methacrylic acidwere changed such that the obtained polymer satisfied a chemicalcomposition, median diameter, and film properties indicated in Table 1and the concentration of the block copolymer added in phase-inversionemulsification was changed so as to obtain a polymer having a particlediameter indicated in Table 1. The results are shown in Table 1.

Comparative Example 2

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, itaconic acid was used instead of methacrylic acid as ahydrophilic monomer and the amounts of monomers were changed such thatthe obtained polymer satisfied a chemical composition, median diameter,and film properties indicated in Table 1, and sodium hydroxide aqueoussolution was used for neutralization in the grafting step duringproduction of the polymer. The results are shown in Table 1.

Comparative Example 3

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that in production of thepolymer, acrylic acid was used instead of methacrylic acid as ahydrophilic monomer and the amounts of monomers were changed such thatthe obtained polymer satisfied a chemical composition, median diameter,and film properties indicated in Table 1, and sodium hydroxide aqueoussolution was used for neutralization in the grafting step duringproduction of the polymer. The results are shown in Table 1.

Comparative Examples 4 and 5

Various operations, measurements, and evaluations were performed in thesame way as in Example 1 with the exception that the mixing ratio ofmonomers compounded during production of the polymer was changed suchthat the obtained polymer satisfied a chemical composition indicated inTable 1. The results are shown in Table 1.

Comparative Example 6

Various operations, measurements, and evaluations were performed in thesame way as in Example 2 with the exception that the concentration ofthe block copolymer added in phase-inversion emulsification in theprocess of producing the polymer was changed so as to obtain a polymerhaving a particle diameter and film properties indicated in Table 1. Theresults are shown in Table 1.

In Table 1:

-   -   “St” indicates styrene monomer unit;    -   “BD” indicates 1,3-butadiene monomer unit;    -   “MAA” indicates methacrylic acid monomer unit;    -   “AA” indicates acrylic acid monomer unit;    -   “IA” indicates itaconic acid monomer unit; and    -   “THF” indicates tetrahydrofuran.

[Table 1]

TABLE 1 Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- pleple ple ple ple ple ple ple ple ple 1 2 3 4 5 6 7 8 9 10 Binder Poly-Type Block Block Block Block Block Block Block Block Block Block compo-mer Aromatic Type St St St St St St St St St St sition vinyl Amount 28.2  37.6  29.1  23.5  37.6  17.9 28.2 22.6 25.0 37.6 monomer [mass %]unit Structure Block Block Block Block Block Block Block Block BlockBlock Conjugated Type BD BD BD BD BD IP IP IP BD BD diene Amount  65.8 56.4  64.9  70.5  56.4  76.1 65.8 71.4 60.0 56.4 monomer [mass %] unitStructure Block Block Block Block Block Block Block Block Block BlockHydrophilic Type MAA MAA MAA MAA MAA MAA MAA MAA MAA MAA monomer Amount 6.0  6.0  6.0  6.0  6.0  6.0 6.0 6.0 15.0 6.0 unit [mass %] Form of NH₃NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ NH₃ salt Median diameter [nm]   266  278   739   448   376   607 428 470 280 125 Solvent Type Water WaterWater Water Water Water Water Water Water Water Film THF gel content  44   45   55   41   40   44 37 35 49 45 properties of [mass %] polymerLoss modulus G″ [kPa]   149  1446   533    6  1031   20 106 87 1362 1490Loss tangent tan δ [-] 0.047 0.212 0.156 0.003 0.173 0.034 0.074 0.0890.235 0.207 Eval- Stationary stability of binder A A B A A B A A A Auation composition Initial viscosity of slurry A A A A A A A A B Acomposition Preservation stability of A A A A A B B B A A slurrycomposition Normal peel strength of A A A A B A A A B A electrodeHigh-temperature peel A B A B A B B B B B strength of electrode Internalresistance of A A A A A A A A A B secondary battery Compa- Compa- Compa-Compa- Compa- Compa- Exam- Exam- Exam- Exam- rative rative rative rativerative rative ple ple ple ple Exam- Exam- Exam- Exam- Exam- Exam- 11 1213 14 ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 Binder Poly- Type BlockBlock + Block Random Block Random Random Block Block Block compo- merRandom sition Aromatic Type St St St St St St St St St St vinyl Amount 37.6  45.0  28.2  34.0  42.3  62.0 62.0 39.0 29.0 37.6 monomer [mass %]unit Structure Block Block + Block Random Block Random Random BlockBlock Block Random Conjugated Type BD BD BD BD BD BD BD BD BD BD dieneAmount  56.4  50.0  65.8  60.0  51.7  34.2 33.0 58.0 46.0 56.4 monomer[mass %] unit Structure Block Block + Block Random Block Random RandomBlock Block Block Random Hydrophilic Type AA MAA MAA MAA MAA IA AA MAAMAA MAA monomer Amount  6.0  5.0  6.0  6.0  6.0  3.8 5.0 3.0 25.0 6.0unit [mass %] Form of NH₃ NH₃ Na NH₃ NH₃ Na Na NH₃ NH₃ NH₃ salt Mediandiameter [nm]   293   214   266   158   163   145 144 302 295 960Solvent Type Water Water Water Water Water Water Water Water Water WaterFilm THF gel content   47   58   44   75   30   91 88 46 50 47properties of [mass %] polymer Loss modulus G″ [kPa]  1453  1504   151 1459  2303  1714 1691 1432 1694 1450 Loss tangent tan δ [-] 0.227 0.3630.052 0.328 0.441 0.718 0.714 0.233 0.256 0.233 Eval- Stationarystability of binder A A A A A A A C A D uation composition Initialviscosity of slurry A A A B A A A C D A composition Preservationstability of A A C B A A B D A B slurry composition Normal peel strengthof A B A B B C D B C B electrode High-temperature peel B B A B C C D B CB strength of electrode Internal resistance of A B A B B C C B B Asecondary battery

It can be seen from Table 1 that in Examples 1 to 14, it was possible toprovide a binder composition for a non-aqueous secondary batteryelectrode that has excellent stationary stability and can form anelectrode having excellent peel strength after exposure to hightemperature and a non-aqueous secondary battery having low internalresistance.

It can also be seen from Table 1 that in Comparative Examples 1 to 3 inwhich the loss modulus G″ and the loss tangent tan δ were outside of theranges according to the present disclosure, it was not possible tosufficiently increase high-temperature peel strength of an obtainedelectrode and it was not possible to sufficiently reduce internalresistance of an obtained secondary battery.

It can also be seen from Table 1 that in Comparative Examples 4 and 5 inwhich the used binder composition contained a polymer having aproportional content of hydrophilic monomer units that was outside ofthe range according to the present disclosure, it was not possible tosimultaneously achieve sufficiently increased high-temperature peelstrength of an obtained electrode, sufficiently reduced internalresistance of an obtained secondary battery, and increased stationarystability of the binder composition itself.

Moreover, in Comparative Example 6 in which the used binder compositioncontained a large polymer having a median diameter that exceeded therange according to the present disclosure, it can be seen thathigh-temperature peel strength of an obtained electrode could not besufficiently increased, and that stationary stability of the bindercomposition itself was poor.

Note that for all of the examples and also for Comparative Examples 2and 3, pressability was evaluated as “good” with regards to “Closeadherence of electrode mixed material layer after pressing” and “Rate ofdensity change of electrode after pressing”. In contrast, in the case ofComparative Examples 1 and 4 to 6, pressability evaluated according tothe aforementioned criteria was not good.

In other words, these evaluation results demonstrate that an electrodefor a non-aqueous secondary battery having excellent pressability wasobtained through a binder composition for a non-aqueous secondarybattery electrode that contained water and a polymer including anaromatic vinyl monomer unit, a conjugated diene monomer unit, and ahydrophilic monomer unit, and in which the polymer had a median diameterof not less than 50 nm and not more than 800 nm, the proportionalcontent of hydrophilic monomer units in the polymer was not less than3.7 mass % and not more than 20 mass %, and the polymer had a losstangent tan δ of not less than 0.001 and not more than 0.80 and a lossmodulus G″ of 1,800 kPa or less.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a bindercomposition for a non-aqueous secondary battery electrode that hasexcellent stationary stability and can form an electrode havingexcellent peel strength after exposure to high temperature and anon-aqueous secondary battery having low internal resistance.

Moreover, according to the present disclosure, it is possible to providea slurry composition for a non-aqueous secondary battery electrode thatcan form an electrode having excellent peel strength after exposure tohigh temperature and a non-aqueous secondary battery having low internalresistance.

Furthermore, according to the present disclosure, it is possible toprovide an electrode for a non-aqueous secondary battery that hasexcellent peel strength after exposure to high temperature and can forma secondary battery having low internal resistance and also to provide anon-aqueous secondary battery that has low internal resistance.

1. A binder composition for a non-aqueous secondary battery electrodecomprising: a polymer including an aromatic vinyl monomer unit, aconjugated diene monomer unit, and a hydrophilic monomer unit; andwater, wherein the polymer has a median diameter of not less than 50 nmand not more than 800 nm, proportional content of the hydrophilicmonomer unit in the polymer is not less than 4.0 mass % and not more 20mass %, and the polymer has a loss tangent tan δ of not less than 0.001and less than 0.40 and a loss modulus G″ of 1,600 kPa or less.
 2. Thebinder composition for a non-aqueous secondary battery electrodeaccording to claim 1, wherein the conjugated diene monomer unit includedin the polymer is a unit derived from 1,3-butadiene monomer.
 3. Thebinder composition for a non-aqueous secondary battery electrodeaccording to claim 1, wherein gel content measured when the polymer isimmersed in tetrahydrofuran is not less than 35 mass % and not more than60 mass %.
 4. The binder composition for a non-aqueous secondary batteryelectrode according to claim 1, wherein the polymer includes an aromaticvinyl block region formed of aromatic vinyl monomer units.
 5. A slurrycomposition for a non-aqueous secondary battery electrode comprising: anelectrode active material; and the binder composition for a non-aqueoussecondary battery electrode according to claim
 1. 6. An electrode for anon-aqueous secondary battery comprising an electrode mixed materiallayer formed using the slurry composition for a non-aqueous secondarybattery electrode according to claim
 5. 7. A non-aqueous secondarybattery comprising a positive electrode, a negative electrode, aseparator, and an electrolyte solution, wherein at least one of thepositive electrode and the negative electrode is the electrode for anon-aqueous secondary battery according to claim 6.